Electromagnetic radiation is well known in the art to be effective for skin disorders treatment and also for hair removal. Goldman in 1963 experimented with a newly invented 500 microsecond duration 694 nm wavelength ruby laser on human skin. He noted that the darker skin color absorbed more radiation and attributed the observations to selective absorption by melanin. Polla and Dover in separate studies during the 1980s demonstrated that the Q-switched ruby laser targets individual melanosomes. The damage was found to be pulse-width dependent: shorter pulses of about 100 nsec width damage melanosomes much more effectively than long pulses of about 100 microseconds. This is consistent with the theory of selective photothermolysis, which states that the pulse duration of an emitted laser wavelength must be less than the thermal relaxation time of the targeted object.
Another application of electromagnetic radiation to skin disorder treatment is removal of vascular lesions. Based upon pioneering work of Anderson and Parrish in the early 1980s, several vascular-specific laser systems were developed using principles of selective photothermolysis. Laser irradiation can selectively destroy specific chromophore targets within the skin by using a combination of appropriate wavelength and pulse duration. Pulse duration must be less than the targeted chromophore's thermal relaxation time—the time necessary for the target to cool by half of its peak temperature after laser irradiation. Since wavelengths corresponding to absorption peaks for various skin chromophores are known, absorption of laser energy can be localized without damaging neighboring structures. The targeted chromophore for vascular lesions is intravascular oxyhemoglobin, so thermal damage is largely restricted to cutaneous blood vessels. For vascular lesions treatment a variety of laser sources have been utilized, starting from a short pulse 575 nm dye laser up to 1064 nm Nd:YAG laser with tens milliseconds pulse duration. The required energy fluence for typical procedure is on the scale of 10 to 50 J/cm2 with about 1 hertz repetition rate.
Laser hair removal is based on the principle of selective photothermolysis, in which energy is delivered to the treatment area in such a manner as to maximize tissue damage to the hair follicle without damaging the skin epidermis and surrounding tissue. Melanin pigment makes a logical target chromophore, because it's most abundant in the hair bulb, which is believed to be the most important target for hair removal; it's much less abundant in the epidermis, even in dark-skinned patients; and it absorbs well in the wavelength range between 600 and 1100 nm. With selective photothermolysis, both the wavelength and pulse duration should be such that laser energy will target melanin in the hair follicles without damaging the adjacent structures, including melanin in the epidermis. The optimum pulse duration should be longer than the thermal relaxation time (the time it takes for half the heat energy to be conducted away from a target tissue) of the epidermis, allowing heat energy to be conducted away, but shorter than the thermal relaxation time of the hair follicle, confining the heat to this structure. The thermal relaxation time is related to the square of the diameter of the target structure: less than 1 msec for epidermis, and 10 to 50 msec for hair follicles depending on the diameter of the hair shaft.
Cooling the skin helps to dissipate heat away from the epidermis, leaving the deeper hair follicles vulnerable. Longer pulses enhance heating and broaden the zone of thermal damage around the follicle. Typically fluences in the range of 20 to 80 J/cm2 are required within a pulse or a train of few pulses with pulse width on the scale of 10 msec.
A large variety of electromagnetic radiation sources are utilized for the abovementioned procedures. Among them are diode lasers, pulsed ruby laser, Nd:YAG laser, alexandrite laser, and non-coherent flash lamp sources with appropriate spectral filters. A high energy flash lamp is disclosed in U.S. Pat. No. 6,280,438 by Eckhouse, et al, entitled “METHOD AND APPARATUS FOR ELECTROMAGNETIC TREATMENT OF THE SKIN, INCLUDING HAIR DEPILATION” (2001).
This configuration of linear flash lamp inside a reflector is commonly utilized in flash-lamp based systems for skin treatment. The flash lamp radiation is delivered to the treated area by multiple reflections from the reflector surface.
A disadvantage of this prior art system is that the reflections significantly reduce the efficiency of the light transfer from the flash lamp to the treated area.
Another disadvantage of this prior art system is that the flash lamp has to be water-cooled in order to dissipate the energy absorbed in the flash lamp tube material.
Another disadvantage of this prior art system is that the long lamp dimensions and the reflector geometry do not allow focusing of the light to smaller spot sizes with respect to the reflector output aperture.
Still another disadvantage of this prior art system is that the lamp's long arc makes it very difficult to change its output beam size by optical means.
The output spectrum of a flash lamp depends on the energy density imposed on it. The radiation of the arc lamp can be modeled by black body radiation. The radiation emitted at a given wavelength λ per unit area can be written in the following way:
            L      ⁡              (        λ        )              =                            2          ⁢          π          ⁢                                          ⁢                      c            2                    ⁢          h                          λ          5                    ⁢              1                              exp            ⁡                          (                              hc                ⁢                                  /                                ⁢                λ                ⁢                                                                  ⁢                kT                            )                                -          1                      ,                where c=2.998 108 m s−1 is the speed of light,        h=6.626 10−34 m2 kg s−1 is Plank's constant,        k=1.38 10−23 m2 kg s−2 K−1 is Boltzmann's constant, and        T is the source temperature.        
The total emitted radiation within a given spectral range is given by:
      P    =          ɛ      ⁢                        ∫                      λ            1                                λ            2                          ⁢                              L            ⁡                          (              λ              )                                ⁢                      ⅆ            λ                                ,                where ε is the source emissivity. The total emitted power is given by:P0=εσT4S,        where σ=5.67 10−8 J K−4 m−2 s−1, and S is the source radiating area.        
With reference to FIG. 1A, curves 121, 122, and 123 represent the radiation spectral distribution for various input power levels (P) for a black body source mimicking a typical flash lamp with 3 mm arc diameter and 50 mm arc length. The emissivity value of such a source is about 0.02, while the input energy to light conversion efficiency is about 90%. One can easily see that for higher input power the emission spectrum shifts towards lower wavelengths in the UV (ultra violet) region. Since only the emission within a preselected spectral band (about 550 to 1200 nm) is used for skin treatment procedures, the total system efficiency decreases the more energy is wasted in UV wavelengths.
The efficiency of a flash lamp within the 550 to 1200 nm spectral region versus the input power is shown in the FIG. 1B by curve 124. The input energy to radiation conversion efficiency in the relevant spectral region decreases for higher input power. For low input power the efficiency drop is even more dramatic. The efficiency value depends only on momentary power value and not on average power.
In order to overcome these difficulties and to improve the spectral distribution of the source, the present invention utilizes a smaller arc lamp with built-in reflector, the lamp supplied by a train of smaller pulses.
For pulsed operation of arc lamps, the pulse shape strongly deviates from a rectangular shape, due to electronic power supply design difficulties. In FIG. 2A, curve 241 shows a typical pulse shape for a prior art flash lamp operated by pulsed electronic power supply. Since the emission spectrum depends on the momentary power of the source, both the high power peak and the low power tail have very low efficiency while still consuming external energy and generating excess heat in the system. Moreover, the low power tail generates excess heat in the tissue without causing a significant effect, since its power is below the required threshold for a procedure. The high peak effect is even worse, since it can cause unwanted tissue damage while exceeding the maximum power applicable for a certain procedure.
The present invention applies a series of short pulses (plot 242 in FIG. 2A) in order to create a more temporally homogenous pulse and as a result, a more homogenous power distribution. In this way both physiological obstacles of uncontrollable power level during the pulse, as well as the system electrical and cooling efficiencies, are significantly improved.
For illustration, the efficiencies of a single pulse used in prior art (curve 241 in FIG. 2A) and the overlapping pulses train of the present invention (curve 242 in FIG. 2A) are compared. The emission intensity (using arbitrary units—AU) for both 550 to 1200 nm and 340 to 400 nm spectral windows are shown in FIG. 2B by curves 244 and 243 respectively. Due to different energy conversion efficiencies, the emission temporal profiles in both spectral ranges vary significantly.
The reason for that variance is shown in FIG. 2C by curves 246 (550 to 1200 nm) and 245 (340 to 400 nm), representing the conversion efficiencies for both ranges. While the peak power drops down after the electronic pulse maximum, the efficiency increases and this causes a long time tail in the 550 to 1200 nm range emission (curve 246). The present invention utilizes a series of short overlapping pulses similar to those in curve 242 in FIG. 2A. Due to more uniform distribution of the power, the total efficiency enhancement is in the range 20 to 50%.
Many disadvantages of prior art flash lamps, including the issues described earlier in this section, are advantageously solved in the present invention. A partial list follows:
In prior art the pulse shape and as a result the output spectrum, does not match exactly the requirements of the medical procedures and precise control of them is extremely hard to achieve because of complex electronic design. It is an object of the present invention to overcome this by applying a plurality of short pulses that enable independent control of the average power during the pulse while keeping the momentary power constant.
In prior art the life expectancy of the flash lamp was limited due to pulse shape with high peak power. It is a further object of the present invention to overcome this by employing a plurality of shorter pulses with combined power significantly lower than prior art pulses of the same energy.
In prior art the irradiated area is controlled by a mechanical shutter, causing energy losses and preventing further light concentration. It is a further object of the present invention to overcome this by providing an arc lamp with integrated reflector to produce an output light that is directional with low divergence. This design enables simple optical manipulation of light, with improved focusing, beam shaping, fiber coupling, and the like.
In prior art, the beam of light is filtered to remove undesired wavelengths. It is a further object of the present invention to provide more control of the output spectrum, thereby reducing the need to filter and improving beam efficiency.
It is yet another object of the present invention in this regard to enhance the output spectrum by providing one or more secondary light sources, thereby increasing the efficiency of the device for treatments requiring the area of the spectrum that the secondary light sources enhance.
In prior art, changing and inserting filters and fluorescence conversion elements is difficult or impossible due to the filter location in the reflector area. It is a further object of the present invention to overcome this by generating a focused, substantially collimated (parallel) beam of light that over which it is easy to attach various treatment heads comprising filters, lenses, reflectors, fiber optics, and/or various other auxiliary components.
In prior art the lamp's long arc makes it very difficult to change its output beam size by optical means. It is a further object of the present invention to overcome this by improved optical beam shape adjustment, whereby the output beam can be adjusted optically according to the needs of the treatment.
In prior art, the flash lamp utilizes water cooling for heat removal, requiring a complicated system for this purpose. It is a further object of the present invention to overcome this by employing arc lamps, thereby enabling operation at equal performance levels while using air cooling, which is much easier to provide.
In prior art, heat removal from the skin is performed by an expensive, poor-conductivity optical window, with the removal performed at the time of treatment, which can be counterproductive to the treatment. It is a further object of the present invention to overcome this by providing high-conductivity thermo-electric coolers that conduct the heat from the skin before or after the treatment.
It is yet another object of the present invention in this regard to provide one or more drum applicators in contact with the skin and containing cooling and/or therapeutic liquid or gel, thereby applying the liquid or gel as the device is moved across the skin.
In prior art, there are no effective positioning aids for accurately positioning the device as it is moved across the skin. It is a further object of the present invention to provide a position feedback device that can, when the application window is moved a predetermined amount, either notify an operator or automatically trigger the next treatment.
It is yet another object of the present invention in this regard to provide spring-mounted pins that mark points on the skin when the device is applied and which points can then orient the device window for the next application.